Corrosion inhibiting with combinations of zinc salts,and derivatives of methanol phosphonic acid



United States Patent O 3,532,639 CORROSION INHIBITING WITH COMBINATIONS OF ZINC SALTS, AND DERIVATIVES OF METH- ANOL PHOSPHONIC ACID George B. Hatch, Allison Park, Pa., assignor to Calgon Corporation, Pittsburgh, Pa. No Drawing. Filed Mar. 4, 1968, Ser. No. 709,951 Int. Cl. C23f 11/10, 11/16 U.S. Cl. 252-389 Claims ABSTRACT OF THE DISCLOSURE Novel combinations of zinc salts and derivatives Of methanol phosphonic acid or methanol diphosphonic acid are used in small concentrations to inhibit corrosion in aqueous systems.

BACKGROUND OF THE INVENTION This invention relates to corrosion inhibitors for aqueous systems. In the past, the corrosion inhibitors in most widespread use have contained either inorganic polyphosphates or chromates, while the polyphosphates have a tendency to hydrolyze and revert to orthophosphates, the waste disposal problems posed by toxic chromate containing corrosion inhibitors have resulted in increased demand for corrosion inhibitors of a completely different class.

Certain derivatives of methanol phosphonic acids have been disclosed in the literature. Alkyl and aryl alpha hydroxyphosphonic acids and salts thereof long have been known. See for example, Monatsch 5, 120,627 (1884); J. Am. Chem. Soc. 42, 2337 (1920); J. Am. Chem. Soc. 43, 1928. (1921); Belgian Pat. 678,912. See also U.S. Pat. 3,122,417 and U.S. Pat. 3,214,454. U.S. Pat. 3,159,581 shows the use of such compounds in detergent compositions. Also of interest are Belgian Pats. 655,166 and 672,- 168. In U.S. Pat. 3,122,417, mentioned above, a series of alkyl alpha-hydroxy 1,1 diphosphonic acid is disclosed. The distinctive common feature Of the compounds of present interest is the presence of one ormore alpha-hydroxy phosphonic acid groups. These groups may be represented by the following formula:

OH i OH where R is H, a lower alkyl group or OOH 2 SUMMARY OF THE INVENTION I have discovered that combinations of zinc salts with compounds containing one or more methanol phosphonic or methanol diphosphonic groups or soluble salts thereof provide excellent inhibition of corrosion of metals, particularly iron and steel, in aqueous systems.

Some particular compounds which are useful in my invention may be represented by the formula T OH OH where R is independently selected from the group consisting of H, alkyl groups up to four carbon atoms, phenyl, and phosphonate groups, R is hydrogen, an alkyl group having up to four carbon atoms Or where n is 0 to 8, and water soluble salts thereof.

The effectiveness of combinations of zinc sulfate with the sodium salts of the methanol phosphonic acids is shown in Table I. The zinc sulfate additions were calculated to supply zinc in amounts equal to 30% of the sodium methanol phosphonate concennations. These examples as well as all the examples in this disclosure, were obtained by immersing steel samples in the solutions described under agitation for five days at 35 C. The pH in Table I was 6.8. Weight loss results are stated in terms of milligrams per square decimeter per day.

TABLE I.-INHIBITION OF CORROSION OF STEEL BY COMBINATIONS 0F ZINC SULFATE WITH COMPOUNDS Weight loss (m.d.d.)

Sodium Sodium Zinc (sul- Sodium dimethyl pheuyl PhoSDhonate fate) cone. methanol methanol methanol conc. (p.p.m.) (ppm. Zn) phosphonate phosphonate phosphonate Table II shows the effectiveness of combinations of zinc sulfate with compounds containing methanol diphosphonate groups. The quantities of zinc supplied were equal to 30% of the methanol diphosphonate concentrations.

TABLE Il'.INHIBITION OF CORROSION OF STEEL BY COMBINATIONS OF ZINC SULFATE WITH COMPOUNDS CONTAINING METHANOL DIPHOSPHONATE GROUPS Weight loss (m.d.d.)

Methyl Sodium Sodium Sodium di- Sodium tetra- Zine (sulmethanol diphenyl methylene bis methylene bis methylene bis Phosphonate fate) conc. phosphonic methanol di- (methanol di (methanol di- (methanol dicone. (p.p.m.) (ppm. Z11) ac phosphonate phosphonate) phosphonate) phosphonate) They may be considered as methanol phosphonic acid Or where R is as methanol diphosphonic acid groups.

The influence of the zinc in combination with ethanol 1,1'-diphosphonic acid is shown in Table III. Zinc in amounts equal to 30% of the ethanol 1,1'-diphosphonic acid (EDP) was added as the sulfate. Inclusion of zinc markedly improves the inhibitive action of the ethanol 1,l-diphosphonic acid.

TABLE IIL-INHIBITION OF CORROSION OF STEEL WITII ETHANOL 1, l-DIPI'IOSPHONIC ACID (EDP) AND INFLU- ENCE THEREON ON ZINC Weight loss (n1.d.d.)

E DP concentration (p.p.m.)

NATE) AND INFLUENCE? ggl fiREON OF ZINC Weight loss (m.d.d.)

With zinc (30% of Diphosphonato conc. (p.p.m.) Alone diphosphonate) TABLE V Influence of zinc (ZnSO on inhibition of corrosion of steel at a fixed ethanol 1,1-diphosphonic acid level (10 p.p.m.) pH=6.87

Zn conc. (percent of EDA conc.): Weight loss (m.d.d.)

The combination of zinc with the substituted methanol phosphonic or diphosphonic acid compounds provides very eifective inhibition of the corrosion of iron and steel over a rather wide range of pH as is illustrated by the data for the zinc-ethanol 1,1-diphosphonic acid combination in Table IV. Inhibition starts to fall off as the pH is lowered to 5 so that appreciably lower pH levels are undesirable. Inhibition tends to fall off somewhat when the pH is raised much above 9, although it remains appreciable at pH 10.4 or above.

The methanol phosphonic and diphosphonic acid compounds are corrosive to copper and copper alloys. The presence of zinc markedly inhibits the corrosive action of these methanol phosphonic and diphosphonic acids with regards to copper and its alloys.

Table VII shows the effect of 50 p.p.m. ethanol 1,1- diphosphonic acid on the corrosion of copper at several pH levels and the influence thereon of 15 p.p.m. of zinc (added as the sulfate). The ethanol 1,1'-diphosphonic acid accelerates the attack throughout the pH range of 4 to 9. 15 p.p.m. zinc (30% of the EDA concentration) counteracts this accelerative action of the ethanol 1,1- diphosphonic acid at a pH of 6, while at higher pH levels the mixture becomes inhibitive with respect to copper.

TABLE VII.-INFLUENOE OF pH ON CORROSION OF OOP- PER AND EFFECT THEREON OF ETHANOL 1,1-DIPHOS- PHONIC ACID (50 p.p.m.) AND MIXTURE THEREOF WITH ZINC (15 p.pm.)

Weight loss (m.d.d.)

3 50 p.p.m. EDP,

Untreated 50 p.p.m. EDP 15 p.p.m. Zn"

Where lower pH values are involved or where even greater inhibition of corrosion of copper and copper alloys is desired, we have found that this may be accomplished by incorporation of the specific copper inhibitors described by Hatch in US. Pats. 2,941,953 and 2,742,369 with the methanol phosphonates or diphosphonates and zinc. These specific copper inhibitors include 1,2,3 triazoles (US. Pat. 2,941,953) (e.g. benzotriazole) and the thiols of thiazoles (e.g. 2-mercaptobenzothiazole), oxazoles (e.g. 'l-mercaptobenzoxazole) or imidazoles (e.g. 2-mercaptobenzimidazole) (US. Pat. 2,742,369).

Concentration levels of 0.05 to 5 p.p.m., preferably 0.5 to 2 p.p.m., of these triazoles or thiols should be employed when they are used in conjunction with the methanol phosphonate or diphosphonate and zinc inhibitors.

I may use any inorganic zinc salts capable of forming zinc ions in solution, i.e. water-soluble salts. Examples of such zinc salts are zinc chloride, zinc acetate, zinc nitrate, and zinc sulfate. I prefer to use zinc sulfate because it is readily available, economical and not excessively hydroscopic.

The ratio of zinc to organic phosphonate compound may vary from about 1:10 to about 1:2, by weight. Preferably the zinc will be about 20% to 40% of the weight of the organic phosphonate. Where triazoles or thiazoles as described above are used, they may be present in the inhibitor composition in amounts up to 10% by weight, preferably between 1 and 5%. Within the limits of these ranges, the concentrations of my inhibitor combination may vary from about 5 p.p.m. to 0.2% or more. At least about 5 p.p.m. of the inhibitor combination should be present in the aqueous system. Concentrations above p.p.m. generally do not significantly improv? the inhibition rate in cooling water and are unnecessary.

My inhibitor compositions are useful in such aqueous solution systems as cooling waters, heating systems, and certain process and distribution systems.

I do not intend to be restricted to the above illustrated specific examples. My invention may be otherwise practiced within the scope of the following claims.

TABLE VI.INHIBITOR. OF CORROSION OF STEEL AT SEVERAL pH LEVELS WITH ETHANOL 1,1 -DI PHOSPHATE ACID AND ZINC (SULFATE) Weight loss (m.d.d.)

Zn+ cone.

EDP cone. (p.p.m.) (p.p.m.) pH 4.9-5.1 pH 6-6.2 pH 6.8-7 pH 7.9-8.1 pH 9-9 2 pH 10.2-10.4

I claim:

1. Composition useful for inhibiting corrosion in aqueous systems, consisting essentially of one part by Weight zinc in the form of a water soluble zinc salt and from 1 to parts by weight of a water-soluble organic phosphonate compound having the formula Ill:

HO-?-R2 P=O OH OH where R is independently selected from the group consisting of H, alkyl groups up to four carbon atoms, phenyl, and phosphonate groups, and R is selected from the group consisting of hydrogen, alkyl groups having up to 4 carbon atoms and where n is 0 to 8, and water-soluble salts thereof.

2. Composition of claim 1 in which the water-soluble zinc salt is zinc sulfate.

3. Composition of claim 1 in which the methanol phosphonate derivative is ethanol 1,1-diphosphonic acid or water-soluble salt thereof.

4. Composition of claim 1 in which the weight ratio of zinc to the methanol phosphonate derivative is about 1 to 10 to about 1 to 2.

5. Method of inhibiting corrosion in aqueous systems comprising adding to said aqueous system at least about 5 parts per million of the composition of claim 1.

6. Method of inhibiting corrosion in aqueous systems comprising adding to said aqueous system at least about 5 parts per million of the composition of claim 2.

7. Method of inhibiting corrosion in aqueous systems comprising adding to said aqueous system at least about 5 parts per million of the composition of claim 3.

8. Method of inhibiting corrosion in aqueous systems comprising adding to said aqueous system at least about 5 parts per million of the composition of claim 4.

9. Composition of claim 1 including a copper corrosion inhibitor selected from the group consisting of l, 2, 3 triazoles, thiols of thiazoles, oxazoles, and imidazoles, said copper corrosion inhibitor being present in an amount up to about 10% by weight.

10. Method of inhibiting corrosion in aqueous systems comprising maintaining therein an amount of the composition of claim 9 to provide up to about 5 ppm. copper corrosion inhibitor.

References Cited UNITED STATES PATENTS 3,483,133 12/1969 Hatch et al 252389 LEON D. ROSDOL, Primary Examiner I. GLUCK, Assistant Examiner US. Cl. X.R.

2l-2.7; 252-855, 387; 260502.4; l06l4 Disclaimer 3,532,639.Ge01'ge B. H atch, Allison Park, Pa. CORROSION INHIBITING WITH GOMBINATIONS OF ZINC SALTS, AND DERIVA- TIVES OF METHANOL PHOSPHONIC ACID. Patent dated Oct. 6, 1970. Disclaimer filed Aug. 10, 1972, by the inventor, the assignee, UaZgon Corporation, assenting. Hereby enters this disclaimer to claims 1 through 10 of said patent.

[Oficz'al Gazette Febmary 1.9, 1974.] 

